nodePadding property

The padding between nodes in a sankey diagram or dependency wheel, in pixels. For sankey charts, this applies to the nodes of the same column, so vertical distance by default, or horizontal distance in an inverted (vertical) sankey.

If the number of nodes is so great that it is impossible to lay them out within the plot area with the given nodePadding, they will be rendered with a smaller padding as a strategy to avoid overflow.

API Docs: https://api.highcharts.com/highcharts/series.dependencywheel.nodePadding